Emergency Supply of Subsea High Pressure Control Fluid Six Shooter

Abstract

Abstract An overview of the design and functionality of the Oceaneering subseaaccumulator or Six Shooter is provided. The Six Shooter was developed as asolution to the historical challenges of BOP emergency intervention. ROVtooling for subsea Blowout Preventer (BOP) intervention has been limited tosmall hydraulic pumps which require substantial amounts of time to operate BOPrams. With faster closing times recommended for emergency intervention, supplementary accumulated volume is required subsea. The Six Shooter can belaunched from a support vessel, IMR vessel or Rig, eliminating the need forcostly Rig or BOP modifications. The unit can be deployed onto a customdesigned mudmat or an existing structure. When deployed, the Six Shooter would allow a ROV (Remotely Operated Vehicle) ofopportunity to function and provide high flow (100 gpm) and pressure (5000 psi)to the BOP via a flying lead. At these flow rates, the industry standardspecifications of 45 second ram closures can be obtained. Equipped with dual regulators, the output pressure of the Six Shooter can beselected with the turn of a ROV valve. Depending on the number of BOP functionsthat need to be closed during an emergency situation, additional units can beeasily added with standard high flow flying leads to increase the usablevolume. The subsea accumulators are constructed with materials that allowdependable and repeatable functioning over long exposures to a subseaenvironment. Introduction Industry standards continue to become more stringent and require a secondarywell control system that can be accessed by the ROV, (Remotely OperatedVehicle) and is able to close critical rams in less than 45 seconds. ROV pumpsare not capable of producing the combined flow and pressures required, therefore a high pressure, high volume system is required. One option might bea complete secondary set of accumulators mounted to the BOP and controlledsubsea. However, there are restrictions on the weight of the BOP stack, andthis solution is not suitable in many cases. Therefore, a modular independent accumulator system that can be launched andtemporarily parked on the sea floor during a drilling campaign is ideal. Thisflexibility allows the operator to forgo costly modifications to the BOP stackand drilling rig. Oceaneering has designed and built an independent subseaaccumulator system that can be deployed onto a subsea structure (mudmat, pile, existing structure, etc...) and connected to the BOP via ROV. The Six Shootercan override functions in the event topside communication is lost on the rig. This unit can be launched from a support vessel, IMR vessel, or Rig allowingany ROV of opportunity to function it. Closing times with this equipment canmatch the closing times of the original BOP stack design specifications. TheSix-Shooter module is constructed with materials that allow dependable andrepeatable functioning over long exposures to a subsea environment.